Cowl muffler for aeroplane engines



Oct. 6, 1931. A, c HEwlTT 1,825,794

COWL MUFFLER FOR AEROPLANE ENGINES Filed Oct. 30, 1929 INVENTQR ufS/tle; a Iz'wzii) patented Oct. 6, 1931 UNITED STATES PATENT OFFICE ASHLEY C. HEWITT, OF ESSEX FELLS, NEW JERSEY, ASSIGNOR TO ENGINEERING DEVELOPMENT ASSOCIATES, OF PLAINFIELD, NEW JERSEY, A CORPORATION OF DELAWARE COWL MUFFLER FOR AEROPLANE ENGINES Application filed October 30, 1929.

This invention relates to improvements in a mufller eductor c'owl for aeroplane engines, and it consists in the novel features, which are hereinafter described.

One of. the objects of my improvement is to utilize the cowl of an aeroplane engine as a muffler for the exhaust gases from the engine, thereby deadening the noise of the exhaust.

Another object of my invention is to employ my mufller-cowl also as an eductor for the cooling air acting on the engine when the aeroplane is running at normal or low speeds, and when the plane is running at high speeds to employ the stream of cooling air for educting the exhaust gases from the muffler, thereby reducing the back pressure on the engine and increasing the efficiency thereof.

A further object of my invention is to provide an annular Venturi throat for the-enhanced eduction of the cooling air by the discharge from the muffler-cowl at normal and low speeds of the plane and for causing the cooling air more effectively to educt the exhaust gases from the muffler cowl at high speeds of the plane.

A still other object of my invention is to have my muffler eductor cowl securely positioned or mounted and to be relatively simple, durable and inexpensive.

Other objects and advantages will hereinafter appear.

I attain these objects by the mufller-eductor cowl for aeroplane engines, two forms of which are illustrated in the accompanying drawings or by any mechanical equivalent or obvious modification of the same.

In the drawings,

Fig. 1 is a side elevation of one form of my 4 mulfler-eductor cowl for aeroplane engines;

Fig. 2 is a front end view of the same;

Fig. 3 is a longitudinal section of my muffler-eductor cowl for aeroplane engines on the line 3-3 of Fig. 2, looking in the direction of the arrows andshowing sundry aeroplane parts and engine parts with connections thereof to the muffler in elevation;

Fig. 4-is a cross section of my muffler cowl on the line 4-4 of Fig. 3, looking in the direction of the arrows, omitting the engine Serial No. 403,495.

and aeroplane parts and showing the connections on said mufller em loyed for securing the. interior part of the ody of the muffler to the fuselage of an aeroplane;

Fig. 5 is a fragmentary side elevation of a modification of my muifler-eductor cowl for aeroplane engines including an annular Venturi throat, which is hereinafter described; I

Fig. 6 includes 'a detail in side view and a cross-section of an interior stiffening rib of my muffler cowl.

Like reference numerals refer to like parts throughout the several views.

11 designates the fuselage of an aeroplane, having thereon a propeller 12, an engine 13 and a cowl 14-15, comprising an inner shell 14 and an outer shell 15, which are joined by interior stiffening ribs 16. Brackets 17 are connecting said shell 14 to said fuselage 11 by means of flanges 18 and 19 on'said brackets 17 and suitable fastenings, which are shown in Fig. 4 and are omitted in the other figures of the drawings.

The cowl 1415 is preferably made in two halves, as shown in Fig. 4, and connected by means of flanges or lugs 20, provided on each half cowl, and bolts, not shown. The half shell 14 and half shell of each half cowl may be joined to each other by means of strips 21 at said flanges 20. The cowl 1415 terminates at its inner end in a central cast metal member 31, as shown i-n Fig. 3.

An annular closure ring 22 is employed to seal the passage at the inner end of said member 31, extending between the shells 14 and 15 at the left hand end thereof in Fig. 3; said ring 22 is provided with openings therein for communicating with exhaust conduits 23, leading from the cylinders of said engine 13, whereby the exhaust gas from said engine is discharged into the muffler space, enclosed between said shells 14 and 15, thereby turning said cowl 1415 into a muffler, which s left open at the right hand end thereof in Fig. 3, forming thereat an exhaust passage 26.

A broad annular inlet passage 24 is left between the forward end 11* ofthe fuselage 11 and the leading end of the muffler cowl 1415 at said ring 22, for admitting the headwind to cool said engine 13; an annular outlet passage 25 is also provided at the follower end of the muffler cowl 1415, therebetween and the body of the fuselage l1.

. The outlet passage 25 is of a larger diameter than said inlet passage 24 and somewhat shorter in a radial direction; the headwind fluxes its way through the cooling space 27, which is bounded by the outer surface of the leading part of said fuselage 11 and the inner surface of said shell 14, and leaves the passage 25 at a higher velocity than it has on entering the passage 24; this increase in velocity of the cooling air is due partly to the increase in volume due to the rise in temperature of the air, produced by the heat ab sorbed from the engine cylinders 13, and partly to the eduction normally produced by the discharge of the exhaust gases from the passage 26 of said muffler eductor cowl 141526.

The area of the passage 26 is preferably of such dimensions that the above statement is correct for normal velocities and low velocities of the aeroplane; for extremely high velocities of the aeroplane, as when it is employed for racing, the dimensions of said passage 26 may be such that the velocity of the cooling air issuing from said passage 25 may be higher than the velocity of the exhaust gases issuing from said passage 26, thereby educting said gases from the muflier cowl and thereby producing a reduction of back pressure on the engine.

An excessive back pressure on the engine when the aeroplane has a normal or low vel'ocity is prevented by the magnitude of the interlor space of my mufller eductor cowl between said shells 14 and 15.

The flanges or lugs 20 on my muffler eductor cowl serve for removing the latter from the fuselage without disconnecting the propeller therefrom as when the engines 13 are to be inspected or repaired.

In the modification of my muflier eductor cowl for aeroplane engines, which is shown in Fig. 5, a discharge guide ring 28, which is substantially boat-shaped in cross section, for a purpose, which is hereinafter described, is concentric with the fuselage 11 and secured thereto by means of radial spacing ribs 29 rearwardly of the follower end of said muflier eductor cowl 141526; the outline of the inner side of said ring 28, which faces the fuselage 11, forms with the part of the outline of the latter, which is opposite thereto, a Venturi throat 30 for the discharge passsage 26 of said muflier eductor cowl 14-15- 26, thereby increasing the efiiciency of the latter in educting the cooling air from said space 27 at normal'and low velocities of the aeroplane; at high velocities of the latter the same Vcnturi throat 30 serves to increase the efliciency of the passage 25 in educting the exhaust gases from said discharge passage 26.

To reduce the resistance of said ring 28 to the passage thereof through the air the outline of the outer side thereof is made convex outwardly, as shown, and forming with the said inner side of said ring 28 an outline resembling that of a boat or fish, which is calculated to ofier the least resistance to cleaving the air.

Said ring 28 is preferably hollow and hermetically sealed, and is shown with its blunter edge positioned forwardly and with its sharper edge placed rearwardly as in the outlines of dirigible air ships and for similar reasons.

The increase in efficiency of my mufllereductor cowl roduced by the provision thereon of the l enturi throat 30 more than compensates for the increased resistance to cleaving the air by said ring 28.

Many changes may be made in my mufllereductor cowl for aeroplane engines without departing from the main scope of my invention, and parts of my invention may be used without other parts.

I do not therefore restrict in self to the details as shown in the drawings at I intend to include also all mechanical equivalents and obvious modifications of the same within the scope of my invention.

I claim as my invention and desire to secure by Letters Patent:

1. In a muffler eductor cowl for aeroplane engines an inner cowl shell, an outer cowl shell, coaxial with said inner shell, interior stiffening ribs, disposed in radial planes lengthwise of said cowl shells therebetween and secured thereto, thereby joining said shells to each other, leaving a mufliing space therebetween, a means for establishing a communication between the exhaust of said engines and said space and a discharge passage from said space at the follower ends of said shells.

2. In a mufiler eductor cowl for aeroplane engines an inner cowl shell, an outer cowl shell, each of said shells being made in multiple sections, a means for connecting sections of said inner shell to corresponding sections of said outer shell at a suitable distance from each other, thereby forming multiple sections of said mufiler eductor cowl, a means for detachably securing said cowl sections to each other, thereby inte rating both of said shells and leaving a mufifing space therebetween, a

.means for establishing a communication between the exhaust of said engines and said space and a discharge passage from said space at the follower ends of said shells.

3. In a mufiler eductor cowl for aeroplane engines a fuselage body, for supporting said engines, an inner cowl shell, encompassing said engines and the leading end of said body, forming a cooling space therebetween, an outer'cowl shell, encompassing said inner shell, leaving a mufiling space therebetween, a means for establishing a .zommunication between the exhaust of said engines and said muflling space, a discharge passage from said muflling space at the follower ends of said shells, a member positioned outwardly of said body at said passage and shaped to produce a Venturi throat effect on the discharge from said passage, thereby enhancing the efliciency of said passage in educting the air from said cooling space.

4. In a muflier eductor cowl for aeroplane engines a fuselage body for supporting said engines, an inner cowl shell, encompassing said engines and the leading end of said body, forming a cooling space therebetween, an outer cowl shell, encompassing said inner shell, leaving a mufiling space therebetween, a means for establishing a communication between the exhaust of said engines and said muiiling space, an annular discharge passage from said mufiling space at the follower ends of said shells and an annular member, encompassing said body at said passage and shaped to produce with the outline of said body thereat a Venturi throat effect on the discharge from said passage, thereby enhancing the efliciency of said passage in educting the air from said cooling space.

5. In a muffler eductor cowl for aeroplane engines a fuselage body, for supporting said engines, an inner cowl shell, encompassing said engines and the leading end of said body, forming a cooling space therebetween, an outer cowl shell, encompassing said inner shell, leaving a mullling space therebetween, a means for establishing a communication between the exhaust of said engines and said muflling space, a discharge passage from said muifling space at the follower ends of said shells, a member, positioned outwardly of said body at said passage and shaped to produce a Venturi throat effect on the discharge from said passage, thereby enhancing the efficiency of said passage in educting the air from said cooling space, the outline of said member be ing substantially ship-shaped in cross-section, to reduce the pressure of the headwind thereon, thereby increasing the efliciency of the outfit.

6. In a muffler eductor cowl for aeroplane engines a fuselage body for supporting said engines, an inner cowl shell, encompassing said engines and the leading end of said body, forming a cooling space therebetween, an outer cowl shell, encompassing said inner shell, leaving a muffling space therebetween, a means for establishing a communication between the exhaust of said engines and said mufiling space, an annular discharge passage from said mufiiing space at the follower ends of said shells, an annular member, encompassing said body at said assage and shaped to produce with the outline of said body thereat a Venturi throat effect on the discharge from said passage, thereby enhancing the e ciency of said passage in educting air from said cooling space, and radially disposed spacing ribs, secured to said member and to said body in axial planes, for supporting said member in position.

7. In combination, an air craft engine; means forming a forwardly open air passage around the engine cylinder terminating to the rear of the engine in the form of a constricted Venturi-shaped air passage; and means for conducting the engine exhaust gases and dischargingthem rearwardly into the air adjacent to said constricted air passage approximately in the path of the air and sufficiently close to said path to exercise an entraining effect upon the air.

8. In combination, a radial-type air craft engine; a casing surrounding the engine crank case and exposing the intermediate part of the cylinders; a cowl around the engine and terminating near said casing; and means for conducting the engine exhaust gases and discharging the exhaust gases rearwardly adjacent to air passage to exercise an entraining effect on the air.

9. In combination, a radial-type air-craft engine; a cone-shaped casing in close proximity to the engine crank case; a cowl around the engine, forming with the casing an air passage at the engine cylinders and terminating near said casing to the rear of the engine to form a constricted air passage; said cowl being formed with an annular chamber closed at the forward part and communicating with the engine exhaust and forming a rearwardly pointing discharge opening at the rear end of the cowl for discharging the exhaust rearwardly into the air adjacent to said constricted passage to exercise an entraining effect upon the air.

10. A cowl construction for aeroplanes provided with radial-type, air-cooled, internal combustion engines, said cowl construction having in combination a generally coneshaped casing in close proximity to the crank case of said engine, an outer annular casing having openings aftof the engine cylinders, said cone-shaped casing and said outer annular casing being spaced apart so as to form an annular passage through which air may be directed to cool the exposed cylinders of said engine, and an exhaust manifold formed in said outer casing.

11. A cowl construction for aeroplanes provided with radial-type, air-cooled, internal combustion engines, said cowl construction having in combination a generally coneshaped casing in close proximity to the crank case of said engine, an outer annular casing having openings aft of the engine cylinders, said cone-shaped casing and said outer annular casing being spaced apart so as to form an annular passage through which air may be directed to cool the exposed cylinders of said engine, an exhaust manifold formed in the forward part of said outer casing, and connections between said exhaust manifold and the exhaust ports of said cylinders.

Signed at New York, in the county of New York and State of New York, this 29th day of October, A. 1). 1929.

ASHLE'Y C. HEWITT. 

